Telephone-transmitter.



UNITED STATES PATENT OFFICE:

RALPH O. BROWNB, OF SALEM, MASSACHUSETTS, ASSIGN OR TO JOHN ABBOTT, OF WINCHESTER, MASSACHUSETTS.

TELEPHONE-TRANSMITTER.

Specification of Letters Patent.

Patented May 21, i907.

Application filed April 25, 1906. Serial No- 313,678.

specification.

This invention has relation to telephone transmitters, to wit, those instruments which are designed to cause an electric current or currents to vary in intensity in synchronism or unison with sound waves.

The object .of the present invention is to provide certain improvements in such instruments; first, for increasing their power to vary an electric current, and, second, to render the instrument capable of remaining in permanent operative condition.

As heretofore constructed, telephone transmitters have usually included a series of electrodes arranged in such manner that one of them may be moved against the other with more or less pressure, or both electrodes moved toward and from each other, so as to vary the conductivity of a variable conductor arran ed in the transmitter circuit. In some of t e instruments now in use, a space is left between'the electrodes to contain a suitable mass of granular carbon or e uivalent material, so arranged that any motion of either electrode causes more or less pressure to be brought against it. This variation in pressure gives rise to a so-called microphonic effect, or, in other words, a variation of resistance or conductivity which results in decreasing or increasing the current in the transmitter circuit. These instruments, as heretofore constructed, have several inherent defects. The low resistance of the variable conductor requires the employment of a current of low power, and further, owing tothe ratio of the low resistance to the high resistance of the line, the range of variation effected by the variable conductor is necessarily limited. It would seem at the first thought, that the defect could be overcome by separating the electrodes to a considerable distance and using a larger amount of granulated carbon. EX erience shows that. this does not'remedy tie evil, for the pressures generated by the sound waves impinging upon a diaphragm are necessarily weak, and consequently, with a large mass of granulated material, the pressure applied to one electrode those forms illustrated is not transmitted uniformly through the mass of material, and consequently a very uneven action is the result. Another evil, which is found in transmitters, as heretofore constructed, is what is known as packing that is to say, a settling down'of the granulated material between the electrodes which prevents their movement. It has been at tempted to overcome this evil by hi hly polishing the electrode, for the packing of the granular material is-annoying and deleterious It is possif to the action of the instrument. ble that this packing is aided by what may be a cohering of the granular particles to the surface of the electrode under theaction of the passing current.

I have discovered that by causing the electric current to traverse the granulated carbon or other active material which is used,

nonconducting material such as mica 'or the equivalent. Since the retaining walls may be made very smooth and are free from any in a line substantially transverse to. the line or lines of pressure as a plied by the vibrat By causing the electric action on the particles of carbon, I

am enabled to use a comparative] wide layer of carbon which Wlll not pac and which, owing to its extreme thinness," is able to carry a comparatively large amount of current without heating, since the thin re- I taining walls quickly radiate any heat that is generated- The pressure is applied to. the

active material by transmitting it from the diaphragm to one or both ofthe retaining walls to cause them to vary their position with relation to each other. l a

It will be understood that the inventionis capable of a great variety of embodiments,

u on the drawin s being some of those in which I have embodied it.

Figure- 1 representsin vertical section a resents a rear elevation of the same.

complete transmitter embodying the invention. Fig. 2 represents a rear view of the samewith the back part of the casing removed. Fig. 3 represents the chamber or member which contains the variable conducting material.- Fig. 4 represents a vertical section through the same. Fig. 5 rep- Figs. 6 and 7 represent another form of chamber or member embodying the invention. Figs. 8 and 9 represent another formv in which the containing chamber is made V-sha'ped. Figs. 10 to l irepresent other forms of con-L taining chamber or member embodying the invention.

Referrin to the drawings, I have shown in Figsl 1 and which com'prisesthe cup (1, a front plate I), and amouth piece c screwed into an aperture therein. The plate I) is hollow at its back to. leave an air-space between it and the diaphragm-d, which is held against the plate by springs a e secured to the edge of the plate as shown. The usual gaskets e e are utilized in this construction. Back of the diaphragm and at a. suitable distance therefrom, is

placeda rigid cross barf secured to theback of the plate 6 outside of the diaphragm by any suitable means. Between the bridge and the diaphragm, is placed-a member 9', which is usually called the button. This member contains the variable conductor or variable resistance medium, which, in general practice, takes the form ofgranular car- :bon. This member may be made in a variety of ways to embody the invention. Its simplest form is shown in Fig. 13, in which case it consists of'a thin flattened tube It having electrodes 'hfi at its ends in electric contact with the granular material that is placed therein. The tube may be made of paper or any other non-conducting resilient or flexible 'cuit.

material and is placed between the bridge and the diaphragm so that the lines of pressure from the diaphragm are transverse to a current flowing from one of the electrodes to the other. When sound waves impinge upon the diaphragm, it iscaused to vibrate and its vibrations are mechanically communicated to the walls of the tube or memlzer'to cause a varying pressure to be brought upon the contained active material, whose resist ance is thereby altered to allow more or less current to pass throughthe transmitter cir- The terminals of the transmitter circuit, which are indicated at i, are connected 'in any suitable way with the electrodes h h.

In Fig. 14, the tube is illustrated as being spiral to secure a greater length and high resistance, for it will be understood that the higher .the resistance of the variable material, the greater the variation of resistance under pressure and-the higher the electromotive forcethat may be used. These two forms of chamber or member may be used private country lines that would 2 a' transmitter, the casing ofv insulating frame is.

for inexpensive transmitters, especially on ave a high resistance, for, by their use, the advantage of common battery systems may be obtained even though the member has to vary the re sistance of a circuit of very high resistance. 1 have used them to vary the current in a circuit of approximately 25,000 phms with success and have reason to believe that the current in circuits of a still higher resistance could as readily'be varied by similar forms of the invention. It Will be understood that the invention practically takes the place of both the induction'coil and the transformer button heretofore employed.

, In Figs. 10'and11 is illustrated another embodiment of the invention in which the electrodes 1' j, which maybe of metal foil if desired, are fastened to the inside ends of two mica walls,,attached to the outside of an walls and the sides of the frame forms a chamjberfor containing the active material. This element or containing chamber will belocated approximately as illustrated in Fig. 1,

- and it is to be assumed that one wall will receive the vibrations of the diaphragm and that the opposite wall will be connected toa rigid abutment. It is quite apparent that I may em loy more than two electrodes, as

shown-in ig. "12, there being an electrode [c located midway between those at j j, thus virtually. roducingmicro honeswhicl1,working toget er, are double t e power of one.

Referring to Figs. 3, 4 and 5; the embodiment of the invention there illustrated comprises two resilient or flexible retaining walls 10 10, arranged substantially in parallelism, relatively close together, and secured to a hollow'frame 11 of non-conducting material by frames 12 12. Preferably, although not necessarily, these walls are formed of mica which has a smooth surface. Between the walls 10 10 is placed the active material, which, as stated, preferably consists ofgranular carbon. To the front wall is secured, in any suitable way, a plate 13 having a boss 14, which may be secured by a screw to the center of the diaphragm d. To the rear wall is attached a similar plate 15 having a boss or pin 16 which is adjustably secured to the The space between the ber of flexible or resilient material, one of 7 them may be rigid as illustrated at 18 in Fig. 7, although in this invention it will preferably be made of non-conducting material susceptible of having its surface highly polished.

Or, if desired, this plate or wall 18 may constitute .one of the frames and serve as a solid abutment for a mica wall interposed between it and the active material. Wit h the arrangement shown in Fig. 7, l-mayalso em loy adjustingscrewsll '19 for adjusting t 1e electrodes 17 17 toward and from each other to varv what I may term the normal resistance of the button.

In Figs. 8 and 9, l have illustrated a con struction substantially similar to that shown in Figs. 6 and 7 except that the opposing walls of the button are arranged at an angle to each other to make a \l-shaped'chamber. -With this construction it is practically impossible for the material to pack, since an ex ceptionally heavy pressure only tends to move. the nlaterial up when the pressure is removechthe material falls bhckin perfect working condition. 1 i

Theoperation of the devices illustrated in Figs. 3 to 9 will. be understood from theprevious descriptions. ltmay bestated, however, that in-all of the forms of the invention which i have illustrated, the path of the current is transverse to the lines oi pressure' resulting from the movement of .the dia-' pliragm, and that the-.lehgthfof the path through the granular material is "many times the thicknessof the material. The pressure is not applied, as in ordinary instruments, by

the electrodes, for on the contrary the electrodes are stationary relatively to each other, and the material is compressed between them by pressure applied on lines substantially perpendicular to the lines connecting said electrodes. It is quite apparent that two or more of the buttons, constructed in accordance with this invention, may be arranged on the same or on opposite sides of the diaphragm, or two or more of them maybe adapted to be operated from one diaphragm,

in consequence of which. the transmitter may be used a double instrument.

Although the invention 1s adapted for many uses, it lends itself especially to mod ern common battery systems, for, owing to the high resistance of the button, a great var ation of the current.fl( wn. g through it is e'l'lected to give even more powerful results than where a local battery-and coil are used at the transmitting station. Conductors of high resistance, such. as iron or steel, may be used in telephone lines, since the resistance of the-button may be made very high as compared with the resistance of the line to cause the largest portion of the current in the line to be expended in the button. Hence the button is able -to greatly vary the resistance of the electric circuit as a whole and govern to a considerable extent the amount of -current flowing through it. I v i j By reason of the particular construction of the button, the'variationsin thecurrent are.

sharp and well defined, and, as the result,

the articulation at the receiver'is clear even though the circuit contains a considerable amount of resistance and capacity. This is doubtless due to the factthat the thinness of the layer of carbon. granules enables the slightest vibration. of the diaphragm to effect an even compression of the carbon, and also t0 the fact that the pressure against the earbon causes it to be forced'endwise of the chamber against the electrodes with a vary ing ressure. The layer though thin, is lengt ened between the electrodes to any desired extent, (as illustrated the length of the layer is many times its thickness) to increase its resistanceso that the resistance of the button in a common battery system may be not much, if any,.le ss than the total resist' ance-of the line.

It will be understood that the invention is not limi! ed to the details which I have illus trated and described.

Having thus explained the nature of the invention, and describeda way of constructing and using the same, although without attempting to set forth all of the forms in which it may be made, or all of the modes of its use, I declare that what I claim is:-

' 1. A telephone transmitter, comprising confronting retaining walls of non-conducting material, one movable :toward and from the other under pressure of sound vibrations, a thin layer of granular material between 'said walls, electrodes between said walls in contact with the granular material and sepa rated a distance considerably greater than the thickness of said layer of granular material, all so arranged that the current flows from one electrode to the other through the granular material transversely to the line of trode to the other through the thin layer of resistance material transversely to the lines of pressure from the diaphragm thereon.

3. A telephone transmitter comprising confronting retaining walls of flat non-conducting material forming a thin. s)ace between them, at least one of said walls eing flexible, a thin layer of resistance material in said space, electrodes lessin thickness than said space located therein between the said walls,

and separated a distance much greater than the/thickness of said layer of material to cause thelcurrent to-tr'averse arelativelylong In testimony whereof I have afiixed my path' between them, said electrodes being signature, in presence of two witnesses. v embedded 1n or overlapped by said layer, all RALPH C- BROWNEI;

s0 arranged, that the Vi bration of said flexible wall 'eoxnpressessaid resistance material in Witnesses: lines transverse to the path of thecurrent be- MARCUS B. MAY, tween said electrodes, l A. L., FoLsoM. 

